This invention relates to a novel exposure lighthouse and to a novel method for making a supplemental intensity-correction filter for that lighthouse. A lighthouse of this type may be used, for example, for manufacturing screen structures for cathode-ray tubes, such as color television picture tubes.
Lighthouses and their use for preparing screen structures for cathode-ray tubes are described in the prior art, such as in U.S. Pat. No. 2,817,276 to D. W. Epstein et al and elsewhere. Such lighthouses may include a lens assembly comprised of one or more optical elements and means for projecting a light field from a substantially point light source through the lens assembly and then incident upon a layer of light-sensitive material on the surface of the support for the screen structure.
The prior art notes that the light intensity across the light field at the light-sensitive layer is not uniform due to causes which may be inherent in the geometry of the optical system or may be due to imperfections in parts of the optical system. It has also been found desirable to provide a tailored gradation in brightness in the light field. It has been proposed to correct nonuniformities in the light field and to provide a tailored gradation of brightness by interposing in the lens assembly a intensity-correction filter. One such filter is described in U.S. Pat. No. 3,592,112 to Harry R. Frey. Such a filter may be prepared, for example, by positioning a photosensitive layer containing light-attenuation material in the lens assembly, exposing the layer to the light field from the light source until the layer, upon development, produces a light-attenuating filter which is a negative of the intensity variations in the light field. By employing a dodger or similar expedient, the filter may also provide a tailored gradation of brightness in the light field. After development, this light-intensity-correction filter is returned to its position in the lighthouse where it is used in combination with the particular light source and lens assembly with which it was made.
In many cases, the intensity-correction filter is deficient in some areas thereof. Also in some cases, one may want to make additional corrections to the optical system or one may want to modify the system to prepare other particular screen structures. It is desirable that these corrections and modifications be made without scrapping the intensity-correction filter. It is also desirable that the correction and modification be made at locations where limited equipment and skill capabilities for making filters are available.